During precision grinding operations it is necessary to adjust the grinding cycle of the grinding machine to accommodate changes in the condition of the superabrasive wheel from the time the wheel was last trued or dressed until the time it must be trued or dressed again. In particular, superabrasive wheels, such as known cubic boron nitride and diamond wheels, tend to increase in sharpness as workparts are ground to the point where loss of the abrasive component becomes excessive and destructive of the wheel and tolerance achievable on the workpart.
In the past, such wheel changes have been accommodated both during the rough grind stage involving relatively high wheel infeed rates, e.g. 0.001 inch/second, and the finish grind stage involving relatively low infeed rates, e.g. 0.00025 inch/second relative to the workpart by continuously monitoring electrical power consumed by the grinding wheel drive motor, and inputting signals from a watts transducer used to monitor drive motor electrical power consumption into the microprocessor of the machine CNC control unit which automatically controls and varies the wheel infeed rate so as to keep the wheel drive motor power consumption substantially constant at a set high level for rough grinding and a set lower level for finish grinding.
Also, in the past, a so-called timed spark-out stage followed the rough grind stage and the finish grind stage during which the infeed rate of the wheel is zero relative to the workpart and is maintained until a selected threshold grinding force is reached where no substantive grinding occurs. The rough spark-out stage and finish spark-out stage were timed from the standpoint that an arbitrary time duration was programmed into the machine CNC control unit for each of these stages with no consideration given of the possible different conditions of the wheel that might exist after the rough and finish grind stages from one workpart to the next during a grinding run involving multiple workparts.
Retruing or dressing of the superabrasive grinding wheel was also set or timed to occur at an arbitrary preselected interval, typically after a certain selected number of workparts had been ground, e.g. one truing pass over the wheel for every ten workparts ground. In some applications, this truing procedure does not maintain the condition of the grinding wheel at or near its optimum as a result of variations in the wheel structure, the workpiece structure, or stock removal rate from the wheel or workpiece.
U.S. Pat. No. 3,344,560 issued Oct. 3, 1967, illustrates controlling wheel feed rate by sensing deflection of the grinding wheel spindle and U.S. Pat. 3,555,741 discloses controlling grinding force in response to signals from a proximity gage. In U.S. Pat. No. 3,344,560 a noncontact type of sensing device for spindle deflection controls the length of rough, finish and spark-out periods of the grind cycle.